Prime Minister Malcolm Turnbull said earlier this month that he expects the next federal election would be held around September or October 2016, potentially causing a repeat of the territory's 2004 campaign clash when the national and ACT polls were held in successive weeks.

Since the 2004 election, the ACT has had fixed four-year terms, with elections held on the third Saturday in October.

ACT Electoral Commissioner Phil Green said if writs were issued for a federal election on October 15 next year, provisions in the ACT Electoral Act required the territory's polling date to be moved to the first Saturday in December.

"That is something that we also need to be planning for as a contingency," he told the Legislative Assembly's Justice and Community Safety committee.

"I am hoping that that does not happen, but that is something we have to plan for."

Elections ACT is also making plans for the possibility that the two election dates are held close together but not on the same day. This scenario would see challenges around pre-polling centre locations as the ACT has a ban on political canvassing and distribution of how-to-vote cards within 100 metres of polling places. Federal laws only require a six metre exclusion zone.

"We have had the experience of an election a week away from our election and we understand what we need to do there," Mr Green said.

"There is particularly a question of informing the electors of the fact that there are two elections running almost concurrently, so we have to make sure that people are aware that there are two elections happening and they have got obligations for both elections.

"We will have in place a range of measures designed to cater for the eventuality of the federal election happening near our election date. If we do have to move our election date then we will make all steps necessary to do that."

If the ACT election is moved to December 3 2016, Mr Green said elections staff would have to be employed for the extended period and the commission would have to extend its lease and renegotiate arrangements for polling places around Canberra.

Each change would incur additional cost for the election.

Mr Green, who was first appointed to the role in 1994, said the decision to include the provisional date of the first Saturday in December was made in the early 1990s to separate the timing of overlapping federal and ACT elections. He told the committee the Legislative Assembly could change the date if it was proposed.

As many as 35 per cent of ACT voters are expected to take part in early voting in 2016, as jurisdictions around Australia see more and more voters take part before election day.

"We will be estimating more, and we will be looking at the trajectory both here and in other jurisdictions," Mr Green said. "So 30, 35 in round terms is a guess but... really what we will be doing is ensuring that those pre-poll centres are very well equipped to take very large numbers of voters, just in case."

Electronic voting will take place on the same system used in the ACT since 2001, with some minor changes since the 2012 poll including extra questions to ensure voters casting an informal vote intend to do so.

From the 2016 election, the Assembly will increase from 17 to 25 members.